1. Field of the Invention
This invention relates to a method for scaling scattered ray intensity in multi bulbs X-ray CT by calculation from a detection signal and a multi bulbs X-ray CT apparatus.
2. Background Art
An X-ray CT apparatus detects intensity of X-rays (hereafter referred to as main ray) radiated from an X-ray bulb and going straight through a subject, and forms a cross-sectional image of the subject. At this time, detection of X-rays scattered from the subject (hereafter referred to as scattered ray) and the main ray produces a ghost image on the cross-sectional image resulting in degradation of image quality. Conventionally, the scattered ray incident from an oblique direction to a detector has been screened by placing a collimator beside the detector, but the scattered ray incident from normal to the detector has been unable to be separated. A technique simulating the scattered ray using a Monte Carlo method and removing the scattered ray component from an original signal configuring the image detected by the detector (e.g. JP-A 11-299768 (Kokai) (1999)) and a technique forming a correction data having the scattered component removed by simulation and configuring a high-precision image (e.g. JP-A 2006-334319 (Kokai)) are disclosed.
However, while a intensity distribution of the scattered ray can be estimated from a structure of the apparatus and a shape of the subject by simulating X-ray tracks by the Monte Carlo method, there has been a problem associated with taking a too long time for a purpose tracking only component incident to the detector to produce an error out of the scattered X-ray, because the Monte Carlo method tracks all scattering tracks. Therefore, application to subjects of all types of shapes has been difficult.
On the other hand, for the purpose of shortening measurement time and achieving a high resolution, in these years, an X-ray CT apparatus having multi bulbs has received attention. The multi bulbs X-ray CT apparatus has large effects produced by the scattered ray from other bulbs incident from normal to the detector, and the effects cannot be screened by the collimator. On the contrary, from viewpoint of possibility of improving degradation of image quality by calculating to correct only intensity of a primary scattered ray scattered once in the interior of the subject, the correction using a primary scattering estimation method has been considered to be effective, and a relative intensity distribution of the scattered rays on the detector can be estimated. However, the estimated scattered rays have relative intensity distribution, thus scaling is necessary for correcting really.